Nights are getting colder here in Iowa, and we may get an early frost. Granted, Oct. 10 is the average first frost date for the Cedar Rapids area, so it wouldn’t be extremely early, but the threat of frost means there are some things you can do to continue to get the most out of your garden.
Frost occurs when temperatures in your garden dip below freezing, 32 degrees. Even though the weather forecast may predict that temperatures overnight are going to get below that, if you live in town, or are in a protected spot, or it’s a windy or rainy night, your garden may not experience frost. Or just part of it might. Frost is most damaging when it’s a still, clear night.
Frost kills “tender” annual plants. Those include tomatoes, peppers, impatiens, marigolds, petunias and more. (Perennials have tougher roots and tops, and survive the winter.)
When a light frost threatens—one in which the temperatures dip just below 32 degrees for a short period of time—you can take a few measures to protect your favorite plants for a while longer, such as covering them with sheets.
By comparison, a hard frost, also called a killing frost, is when temperatures get below 28 degrees for several hours. This type of frost kills all annuals, even those that will tolerate a light frost. There’s little you can do to protect annuals from a hard frost.
Now, before our first frost, there are some things you can do to extend the enjoyment of your garden.
• If you have any houseplants still out, bring them in. Even if they’re in a covered area, most don’t like cool temperatures and will sulk and get diseases if you continue to leave them outside. Rinse them off with a gentle spray of water from the hose or the shower to make sure you don’t bring in any bugs.
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• Bring your pots indoors. Put them in the sunniest place you have. Depending on the type of plant, you may be able to enjoy them for weeks or even months longer before they start to get sickly from the lack of light or start to fail because of dry or cold air indoors. Some types plants in pots can indeed survive all winter indoors. Hibiscus, jasmine, rosemary, citrus trees, and others will often survive the winter if given plenty of light and humidity.
• Take cuttings of some plants. Basil, begonias, coleus, ivies, and more root beautifully in a jar of water in a window. Once the roots are about an inch long, pot them up with potting soil. Replant outdoors in spring.
• Pick all tomatoes that are even remotely ripe. If they’re even a little bit red, they’ll finish ripening if you put them in a bright, sunny place. (Don’t store in the fridge. It diminishes their flavor and prevents them from ripening any more.) With green tomatoes, try your hand at some dishes that take advantage of their delightful tartness, like green tomato salsa. There are wonderful recipes easily available online.
• Cut most of your basil. It likes hot weather and will slowly die out in the cool weather preceeding a frost. Take cuttings, as directed above. Or pinch off any flowers and put the cut ends in a jar of water. Cover with a plastic bag and store in the fridge. Or make pesto. Or simply puree the basil leaves with olive oil and freeze in ice cube trays to use in soups and other dishes through the winter. Parsley and cilantro are fine with just a light frost. But they won’t last much longer after that. Cut them and store as you would with basil.
• Pull out diseased annuals and cut back diseased perennials now. After a frost, it’s hard to tell what was healthy and what was not. Dispose of them in some place other than your compost heap. Otherwise, you’ll eventually just be spreading the disease pathogens along with your compost.
Veronica Lorson Fowler is co-publisher of The Iowa Gardener website at theiowagardener.com.